A disc brake device adapted to a vehicle brake device sometimes generates a so-called squeal noise when the brake is applied. This squeal noise is considered to be generated due to a coupled oscillation of the disc plate and the friction pad material and a study has been made focusing on the frictional contact portion between the disc plate and the friction pad material, between which the force transmitting is made (See non-patent literature 1). At the early stage of the study, a model analysis of a contact point where vibration occurs with the same phase and the same amplitude in the friction contact portion was conducted. According to the analysis, a qualitative tendency of the squeal could be represented, but a restoration moment about the contact point could not be taken into consideration and as a result, the qualitative tendency of the squeal did not agree with the quantitative tendency. Accordingly, in order to solve this problem, it is necessary to conduct the model analysis of the contact surface by measuring the stiffness of the dynamic stiffness of the contact surface.
In the non-patent literature 1, as a measurement device for measuring the dynamic stiffness of the contact surface, a device equipped with an oscillation device for oscillating the friction pad material under a pressurized state, a load measurement device which measures the load applied to the friction pad material and an acceleration measurement device which measures the acceleration of the friction pad material generated by the oscillation. This dynamic stiffness measurement device first oscillates the friction pad material with a random wave of squeal oscillation frequency band (1 kHz to 5 kHz) and measures the acceleration speed of the friction pad material generated by the oscillation. Thus, the transfer function (Accelerance) from the force to the acceleration is obtained and the resulted value is converted into the dynamic stiffness. Further, a device similar to the device above is disclosed in the patent literature 1, although the device disclosed therein relates to a measurement device for measuring the spring constant.